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How do planes know what altitude they're cruising at?
I know that when planes enter the aerodome containing the airfield of destination, the ATIS will tell them an altimeter setting so the system knows how to calculate their altitude above their field; what about in cruise? Do they listen to the ATIS of every sector while cruising as well?

To combine the other two answers:
Below the "transition altitude" (which is 18,000 feet in the US, 5,000 feet in Germany), the pilot has to pay attention to the current altimeter setting, and adjust it accordingly. However, they don't have to listen to ATIS/AWOS/etc., most controllers will give you the current altimeter setting when you check in with them, or when you make some request, or when it changes, or sometimes just for no reason at all. If you're not talking to ATC, though, you would have to get the local altimeter settings from ATIS, or satellite weather, or some other source.
If you're above the transition altitude, however, you are supposed to just set your altimeter to a fixed 29.92 inHg or 1013 hPa. The theory is that when you're that high, the distance to the ground doesn't matter. There are no towers to avoid or anything, so you only need to pay attention to the distance between planes. Having one single setting helps relieve the pilots of fast-moving planes from having to constantly adjust their altimeters while still providing vertical separation between aircraft.

It's interesting that Germany would have a transition altitude of 5,000 feet, given that Germany has terrain substantially higher than that.

@NateEldredge It is not 5000 ft everywhere: The definition says 5000 ft AMSL or 2000 ft AGL, whichever is higher. See here for details.

+1 for explaining about transition altitude. I've never flown a plane that high so Flight Levels escaped my answer.

Above Transition Altitude (e.g. this is 5000ft in Germany) the altitude is measured in flight levels (FL) - each FL equals 100ft and is measured above an artificial QNH of 1013,25 hPa.
If you cruise for example at FL380 that will be 38000ft above the pressure level of 1013,25 hPa. This system assures that 2 aircraft which are 10 FL apart (e.g. FL370 and FL380) always have the required separation of 1000ft.
During descent when passing Transition Level you will change your altimeter setting to local QNH which ATC will tell you.

Also nicely illustrated in Altimeter setting procedures

Addendum: which ATC will tell you or which you get from ATIS.

@aCVn Correct, however ATC has to tell you when they clear you to an altitude.

It's possible to fly VFR between untowered airports without ever talking to ATC, so you'd need to pick up altimeter settings from ASOS/AWOS/etc. along the way.  However, if the transition altitude is in class E/G airspace (yes, it can happen), you only need to fuss with that at the start and end of the flight since you're at Flight Levels in between.

In other words, whenever you exceed the local transition altitude, everyone switches their altimeters to standard pressure and leaves them there until they descend again.  Flight levels and aircraft then float up and down with local pressure but they all do so together, maintaining proper separation with respect to each other.

Do they listen to the ATIS of every sector while cruising as well?

Yes, smaller planes listen to ATIS/ASOS/AWOS or ATC while enroute below 18,000 ft (in the US) and adjust the altimeter setting in the Kollsman window accordingly.
These are both set to 29.92 for example

Top one looks like 29.90 to me.

Could be. I claim parallax!

In a word: altimeter. It is a device that measures the pressure of the atmosphere. Flight levels are expressed as height above Mean Sea Level or MSL, a worldwide standard of pressure at sea level at a specified temperature or "standard temperature and pressure". The referenced altimeter reading is actual pressure at the surface.
Altimeters in aircraft can be adjusted to compensate for local variations in the air pressure so that altimeters in all aircraft display approximately the same readings at consistent heights above the surface in the area. Periodic pressure references and adjustments are necessary as air pressure fluctuates due to weather patterns.
Air traffic controllers usually give periodic altimeter settings, especially when first contacted during communication hand-offs. Pilots may also request that information from them. Other sources are ATIS, if a tower-controlled airfield is nearby, En-route Flight Advisory Service (EFAS), and automated weather reporting stations such as ASOS and AWOS.
When attempting to land at a controlled airfield, a wise pilot will listen to the ATIS prior to contacting the approach controller. In instrument conditions, having an accurate altimeter setting (among other things) is critical to operating and landing safely.


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Why do planes above FL290 need more vertical spacing?
At altitudes no higher than 29,000 feet, planes need only 1,000 feet of vertical separation.
However, planes over FL290 need twice that, i.e. they need 2,000 feet of vertical spacing between them and a plane with otherwise insufficient lateral separation.
Why is the extra vertical spacing needed, and why is it needed over FL290 specifically?

The atmospheric pressure changes more rapidly with altitude near the ground than it does higher up.  Assuming an instrument has some error based on determining the difference between two pressures, this error increases with altitude.
Using a standard atmosphere, the pressure difference between 3000 and 4000 feet is 3.3 kPa.  The difference between FL290 and FL300 is 1.4 kPa, less than half.

Pre RVSM
The separation rules you mentioned (1000 ft < FL290, 2000ft > FL290) were inplace due to the reduced accuracy of old altimeters at these altitudes. A less accurate measure meant larger safety margin was required.
Post RVSM
Today, most if not all modern airliners are certified for RVSM (Reduced Vertical Separation Minima). These aircraft are equipped with more accurate altimeters and ADCs (Air Data Computers). RVSM reduces the required separation from 2000 ft to 1000ft at FL290 - FL410. In case of malfunctioning RVSM-related equipment (included in the MMEL) that aircraft must avoid RVSM airspace (= fly lower than FL290) until this equipment is fixed.

You have to be RVSM compliant to fly in RVSM airspace at all, and just about all jets are. If you have an equipment malfunction that has to be MMEL'd to dispatch, and it is one of the RVSM requirements, your are stuck below FL290 for that trip.

@JohnK Thanks for the addition. I'll add that to my answer

check US AIM 4−6−10. Procedures for Accommodation of Non−RVSM Aircraft. Some non RSVM can fly in those air space but on special exception. Certification flight, DOD or foreign government flight are examples.

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Is there a way for passengers to know which runways their flight will use?
When I fly, I like to see the airport when I take off and land. Is there a way I can know, in advance, which runway the plane is likely to depart/arrive from so I know which side of the plane to sit in?

Do you mean you like to see the airport terminal building?

See also Is there a way to find out which runway is used by which flight on a particular day/date? on the Travel Stack Exchange site.

@WildGurgs, What do you do when an airport has parallel runways?

@MikeSowsun yes, and as many RWYs as possible

@CrossRoads Look at the wind patterns, but I'm wondering specifically about airports with cross runways like SFO - I don't know how to predict if I'll land on the 19s or the 28s for example.

They'll land into the wind if possible, unless the wind presents very little tailwind to allow using the preferred runway that will help with noise abatement over populated areas.  You could get an aviation band radio and listen to the tower frequency, or the delivery clearance frequency, or the ATIS even. https://www.faa.gov/air_traffic/weather/asos/?airportId=ksfo Phone in & listen to the airport weather.

No. As far as is reasonably practical, planes land and take off into the wind so the runways that are in use will depend on weather conditions at the time of the flight, as well as traffic and so on.
These things probably won't be known at the time when you're picking your seat.

While you're right, ones best guess could involve looking up the prevailing winds at an airport and booking accordingly. That gives you a decent change of being right.

Since you asked about "likely", then it really depends on the airport.
Some airports have prevailing winds that are quite consistent.  As an example, if you were to fly a domestic flight out of SFO between May and October, you've probably got close to a 90% chance that you'll depart on 1L or 1R, with most of the airport on your left.  SJC is similar.
The weather at many other airports is variable enough that this isn't as likely to work.

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Should I contact ATC if I don't have a transponder?
The flight school I usually rent from is under the shelf of class C airspace. If you're going out to a practice area, the standard procedure is to contact approach control and get a squawk code, so they can better coordinate traffic. However, it's not required, since the practice areas are outside the class C.
At the moment, none of the school's planes have transponders*. One of the instructors said not to contact approach for now, because without a transponder, they wouldn't be able to do anything anyway and it'd just annoy them. On the other hand, during my last practice flight, I heard** them vector an aircraft around some unknown other aircraft. I suspect the unknown aircraft was me, which made me think that it would be better to talk to them after all. That way, I could (for instance) tell them my altitude, and they wouldn't have to vector an aircraft that was (say) 5,000 feet above me. But, back on the first hand, if I'm just a primary contact, they have no way of knowing which blip is talking to them, so maybe they'd have to vector the traffic anyway.
So, in that situation, is it better to contact ATC or not?
* Since this came so soon after the switch to ADS-B, and since it affects all aircraft at the flight school, I rather strongly suspect that they just got a bad batch of ADS-B transponders and had to send them back. That's just my theory, though, I don't know for sure one way or the other.
** I tuned in the approach frequency, even though I didn't contact them.

'they have no way of knowing which blip is talking to them'. There are ways to correlate blips to aircraft on the frequency. For example by giving an unambiguous position report, or by making identifying turns. The blip can then be tagged with the proper identification.

I believe that unless the IFR traffic reported you in sight that they would still be required to vector the other aircraft to maintain lateral separation.  Your verbal reporting of altitude is helpful to enhance their situational awareness, but unless they can verify on their scope the information is “for reference only”.  And even if your mode C is working, if you aren’t talking and squawking you are unverified.  This is the difference between “traffic 12:00, 2500 feet” and “traffic 12:00, indicating 2500 feet.”  If you had no transponder the call would be “reporting 2500...”

@MichaelHall it's actually the opposite, Mode C is advisory to the controller and the pilot report overrides it if there's a gross difference. For the most part altitude separation is a non-radar technique; Mode C altitude only comes into play for separation if aircraft are changing altitude and can't give continuous altitude reports. In that case the Mode C does have to be verified against a previous report.

Every US controller I've ever heard from says they'd prefer to be talking to every aircraft in their airspace, period. This lets them know your intentions and allows them to move you around if needed, which saves them far more time than it costs giving you traffic advisories.
If you don't have a transponder, they can still tag your primary target with your tail number. Since you can't squawk or ident, they'll need to issue you an "identifying turn" or receive an exact position and heading report for positive identification before they're allowed to do that. Once you're tagged, though, you look the same to them as someone with mode A only.
If you're practicing maneuvers, I suggest letting them know what to expect with something like "maneuvering at or below 3500 ft." That's a good idea even if you have mode C, but it's critical without it.

They'd rather talk to you, even if they can't do much for you. If you report over XYZ at 4500 heading east, they can correlate that to a primary target & note that it's N1234S "over there". They may have to call you again if traffic is heading your way at 7,500' to confirm your altitude, but unless they're busy, that's no big deal. And if the targets are pointed at each other, it's a HUGE help for the controller to know he can call YOU, by callsign, and have contact.
During a TRACON tour a couple years ago, they played a tape of scope video + audio of a situation that got really tense because the controller couldn't reach to a VFR target & find out his intentions. Their plea was, call us, let us know you're there.
If the frequency & airspace are really busy with IFR traffic that's well away from you, then that's probably a different case. But that doesn't sound like what you're describing.
Easy enough to call them up, and when things are quiet, ask if they would prefer hearing from you each flight until the transponders get fixed. If they say no, go with that. But I suspect they'll be glad to have you listening on frequency.


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Does the pilot need to keep track of which instructions can be issued by which ATC facility?
Each ATC facility can only issue certain instructions or clearances. For instance, only the control tower can issue landing clearances, and only for that specific airport. Legally speaking, does the pilot need to keep track of what instructions can and can't be given to them based on which facility they're talking to?
For instance, let's suppose that the guy working approach control just recently transferred from the tower, had a brain fart, and accidentally issued a landing clearance to an approaching plane. Let's further suppose that the pilot forgot that he wasn't talking to tower, accepted the clearance, and landed the plane. Obviously the controller is going to get in trouble for that, but is the pilot who accepted the clearance from the wrong facility also in hot water?

Eh, not certain the premise here is correct. "Anything is possible with coordination." It's not unheard-of for someone expecting a visual approach to be shipped to Tower before the approach clearance is issued; TRACON calls on the landline and says "Hey I forgot to clear N123, you can issue the visual approach" and Tower says "N123, cleared visual approach runway 36, runway 36 cleared to land." Or for a surveillance approach, the final controller will say something along the lines of "Tower advises cleared to land."

Also, unless TWR is also asleep in your hypothetical example, they will surely notice a plane on final which they know nothing about, and go "A/C on final, WTF you think you're doing, cancel landing clearance, go around". Followed by a chat with APP to figure out how the hell the plane got there.

@randomhead Yeah, that was my question. So you're saying that, if approach issues me a landing clearance, it's safe to assume that they coordinated with tower (or whoever) and I can just land? (Obviously, if it happened in real life, I'd double-check, but this is a hypothetical.)

Well there's "safe to assume" for certificate action and "safe to assume" for preventing a collision with another aircraft holding on the runway... if you're ever in doubt, definitely double-check. But (again I'm not a lawyer) as far as certificate action goes, I think if ATC gives you an instruction then you have no obligation to doubt the legality of that instruction.

I've issued a landing clearance as Approach before. The Tower controller is sitting right next to me, and sometimes it makes more sense to keep the plane on the approach frequency instead of changing to the tower frequency. So the tower controller will tell me to issue the landing clearance. Never had a pilot be confused by this.

I'm not a lawyer, but I think no. The pilot's responsibility is to comply with ATC clearances (91.123a) and instructions (91.123b), to the extent that the instructions/clearances are compatible with the safe operation of the aircraft. Nothing says that the pilot must evaluate ATC instructions to ensure that ATC is legal to issue them.
If ATC tells a pilot to do something illegal or unsafe, like fly into a cloud when the pilot is VFR, then of course the pilot has the responsibility to reject the ATC instruction. But pilots are not responsible for policing ATC and ensuring that ATC is following their own rules—which can be overlapping and contradictory, not to mention less-than-obvious to a pilot.
For example: in order to use Line Up and Wait, the Tower control position must not be combined with another control position like Ground and the tower supervisor position should not be combined with another position. How is the pilot to know the staffing situation in the cab?
Or: In the Terminal environment, ATC is allowed to use diverging separation with a minimum of 15 degrees between aircraft courses when using one type of radar antenna, but the minimum is 45 degrees when the scope is using a different type of radar. The pilot will have no clue which is in use at any given moment.
An experienced pilot will have some situational awareness and will expect certain instructions/phraseology from certain facilities, but there's a lot happening on the ATC side that pilots don't see—coordination, rules, etc. For example at up/down facilities which are open throughout the night all functions will typically be combined into one single controller working in the tower cab, and there's no rule that the controller can't say

Cleared visual approach runway 36, runway 36 cleared to land, taxi via Alfa to the ramp, remain this frequency and have a good night.

I kind of agree, but Approach issuing a landing clearance would in fact be dangerous. Approach can't see the runway, and doesn't know who else has been cleared on to the runway. It would be good for pilots to know that.

I've been issued landing clearances late at night by controller whom we checked in with as "XYZ Approach" many times. Who subsequently cleared us to taxi to our gate on that same frequency. Not my role to question if that controller is allowed to issue the clearance he just gave me - I've been cleared for an approach, so I fly it; been cleared to land, so I can land, and taxi via {whatever} to the gate, so I do that.  (Also been cleared to taxi, takeoff, & land by controllers who can't possibly see my aircraft due to visibility in the hundreds of feet... I don't ask if their radar is ...

... working & approved for them to use for that purpose!)  Some things you accept that they're following their rules & procedures, that I probably don't know & can't verify. And on that basis, the system works. Well.

@DJClayworth At some airports the approach controller is sitting in the tower, so he absolutely can see the runway.

I refer back to the comment by  @randomhead. Anything can be done with coordination. I was working the midshift on (I guess) a very clear night and had given the arrival a descent clearance. About 50 miles out, the aircraft reported the airport in sight. I called the approach controller to pass along the information. He said, "Clear 'em for the visual approach," which I did.


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How is the VOR-A approach at KVCB meant to be flown?
This is the VOR-A approach into KVCB:

The plate indicates that "Circling NA west of Rwy 2-20." But runway 2 is left traffic and runway 20 is right traffic. How is one meant to avoid the area west of 2-20 to adhere to the requirements of the plate without busting 91.126 by making turns opposite the direction of traffic?

When would you be making turns opposite the direction of traffic?

@MichaelHall Right base for runway 20 and left base for runway 2 are both west of the runway, right? Maybe I'm missing something stupid.

Think IFR vs VFR…

@MichaelHall The FAA has released several interpretations that traffic pattern directions apply to IFR circling approaches: Murphy, Collins, ...

Krug.

I would presume that the published procedure would take precedence.

@MichaelHall Could be. Feels like a pretty oblique way to authorize one to violate a FAR, though.

Not really could be, must be.  Because there isn't an option, the plate says don't circle to the West - that's clear enough.  "Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right."  The approach plate in this case serves the function of indicating which way to turn.

Michael Hall is correct, but I think this could use some clarity. None of the turn requirements of this section (91.126) are applicable because the approach plate “requires” that a pilot not comply. The light signals or visual markings are not relevant. In other words, following a Part 97 procedure cannot cause you to violate a Part 91 requirement.

Very closely related.

IFR flying can be quite dangerous, particularly when transitioning from the airport to the enroute structure and vice-versa. This "answer" should be taken as a discussion more than a definitive statement. See also this previous discussion: Why is the VFR traffic pattern area at some airports different from its IFR circling approach area?

Per the sectional (and AFD), Runway 20 is right traffic while Runway 2 is left traffic. Thus VFR pilots operating at VCB are restricted to remain west of the airport no matter which runway they are using. The AFD further states:

No turns to crosswind below 800' MSL, remain west of interstate
highway for Rwy 20, noise sensitive area west of arpt.

That noise-sensitive area appears to be the communities of Ridgeview and Browns Valley, and seems to present something of a contradiction. If there are noise-sensitive areas to the west of the airport, why should pilots be restricted to remain west? There must be a compelling reason.
As an educated guess only, that compelling reason may be Travis Air Force Base and its associated Alert Area 682. Note how close VCB is to the Travis Class D airspace: an east-of-the-airport pattern would put a VFR pilot uncomfortably close to if not solidly within the surface area, depending on the size of the pattern they flew. And note how the edge of A-682 nearly lies on top of Runway 2–20 at VCB: an east-of-the-airport pattern would be almost entirely within the alert area. Sure, it's not super likely that military trainers would be flying around right on top of another airport's traffic pattern... but if you have the chance to avoid the possiblity altogether, why not do it?
For IFR traffic, however, the calculus changes. An IFR aircraft operating in controlled airspace must be in contact with and under the control of an ATC facility—in this case Travis Approach, who is probably also talking to any military aircraft flying around in the alert area. So the question of violating the Class D is alleviated; I strongly suspect that Travis Approach has to coordinate with Travis Tower prior to clearing an aircraft for the VOR-A at VCB, and furthermore that when an aircraft has been cleared for the approach IFR traffic off of Travis is prevented from turning north- and west-bound.
Even more importantly, look at the sectional and the approach plate. Observe the rising terrain which comes to a peak only seven NM west of VCB at 2800' above field elevation; observe the obstruction only a couple of miles west of VCB at 700' above field elevation. A VFR pilot operating in the traffic pattern can easily see and avoid these obstacles. An IFR pilot executing a circling approach—with the possibility of going IMC and having to execute a missed approach—is in a much more dangerous situation.

Now for the legal aspect: in the Krug interpretation which you linked, regarding a pilot's desire to fly a circling approach contrary to the established pattern direction, the Office of the Chief Counsel said:

ATC may not issue clearance to conduct a right-hand turn at an airport without an operating control tower in Class G airspace. The Collins Interpretation notes that the circumstances under which a deviation from the left-hand turn requirement in § 91.126(b)(1) is "authorized or required" are very limited. Specifically, a deviation must be "authorized or required" by approach guidelines to a specific airport or by another FAA regulation.

(Note that ATC is not only prohibited from issuing circling instructions at Class G airports; they are prohibited from issuing circling instructions at all non-towered airports. This is not to say that pilots are prohibited from electing to circle, or not, on their own accord and to the runway of their choosing. Obviously in the case of a circling-only approach they must circle!)
To my reading of the letter, the approach plate restriction "Circling NA west of Rwy 2–20" is in fact a "requirement by approach guidelines" which supersedes not only the default left-pattern requirement for Runway 2 but also the specifically-published right-pattern requirement for Runway 20.

CFR 91.126 is a general rule that establishes the default of left turns in the VFR traffic pattern, unless right turns are specified.  It is intended to provide safety and consistency in the flow of VFR traffic at non-towered airfields.
IFR Traffic should generally match the flow of VFR traffic when circling, but when you are operating on an IFR clearance you are expected to fly procedures as they are published.  If you have been cleared for an instrument approach that contains a requirement to execute a specific circling procedure different than the VFR pattern, then that is what you are expected to fly.  There is no conflict with the CFRs because you are operating under Instrument Flight Rules, which take precedence.
FAA Advisory Circular AC90-66 confirms this:

8.2.1:  The FAA does not regulate traffic pattern entry, only traffic pattern flow. For example, an aircraft on an instrument approach flying on the final approach course to land would follow the requirements dictated by the approach procedure.

9.6:  Pilots are reminded that circling approaches must comply with § 91.126(b) unless the approach procedure explicitly states otherwise.

How is it meant to be flown then if you cannot circle to the West?  In this particular case I would enter a left base for RW 20, or a right downwind for RW 2.
Additional information can be found here:  IFR Magazine Article

I'm convinced by @randomhead's argument that the requirements of this specific approach plate supersede 91.126, but saying 91.126 doesn't apply at all to IFR operations seems suspect. What do you think about the interpretations I posted in comments on the OP?

KVCB is a non-towered class G airport, if that changes anything.

@757toga, skimming again, but 8.2.1 positively leapt off the page at me:  "The FAA does not regulate traffic pattern entry, only traffic pattern flow. For example, an aircraft on an instrument approach flying on the final approach course to land would follow the requirements dictated by the approach procedure."  This is the entire gist of my answer, distilled right there, by the FAA.

... AND, 9.6 further backs my point!  "Pilots are reminded that circling approaches must comply with § 91.126(b) unless the approach procedure explicitly states otherwise."  I will admit that my answer can be improved by referencing these, and I thank you for that, but nobody I know carries a binder of Advisory Circulars for reference airborne.  Fly what the plate says to do.

Let us continue this discussion in chat.

@757toga, thanks, I added the link to my answer for good measure.


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Changes to aeronautical charts
Are there notes on changes to aeronautical charts available anywhere?
For example, when a new sectional comes out, many changes are charted. Is there any place I could find the specific changes that were made or, even better, documentation on why they were made?

Well there is definitely a source that lists all airspace changes.  More later.

Changes to a chart are almost always changes to the underlying data. The FAA publishes changes via Transmittal Letters or through the National Flight Data Digest.
TLs typically cover changes to procedures…
https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/Transmittal_Letters/
NFFDs typically deal with NAVAIDs, airways, fixes, airport diagrams, etc…
https://www.faa.gov/air_traffic/flight_info/aeronav/Aero_Data/NFDD/
You would probably have to look through several of these for a given ARINC cycle to get a full picture of what is changing.
I do not believe the FAA puts out notices to individual charts (someone please correct me if I am mistaken).

The FAA publishes a Chart Update Manual, or CHUM.  Between major chart revisions, we used to "CHUM our charts," mostly for things like cell phone towers.
Let the FAA be your guide!
General Information:
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/aero_guide/
Chart User's Guide:
https://aeronav.faa.gov/user_guide/20230810/cug-complete.pdf

You've mentioned a Chart Update Manual, but you've linked to the Chart Users' Guide. I don't see anything about a CHUM on this page.

The FAA did not produce the CHUM. The CHUM (and then eCHUM) was obstacle data to be used with charts that were not frequently updated. Nevertheless, that does not exist anymore anyway.


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How precise is the placement of airports on VFR sectional charts?
Looking at the August 10, 2023 edition of the San Francisco VFR sectional, M45's displayed name is being changed from ALPINE CO to ALPINE COUNTY:

More ambitiously, it is apparently going to be moved about 1700 feet west overnight!
Assuming they are not actually going to move the airport, this leaves me to wonder how precise the placement of airports on VFR sectional charts are meant to be.

Is it perhaps just a correction of what had previously been mis-plotted? Maybe using the east-west portion of the creek (just above the letter "A" of "Alpine County" in the lower graphic) as a reference, is the north end of the runway more accurately plotted in the newer version?

@RalphJ Could be. If that's the case, that would be a good answer to my question, or at least part of one. Though the coordinates in the chart supplement haven't changed.

@RalphJ Looks like that's the case! It does make me wonder why the coordinates in the CS haven't changed in concert, though.

Lucky guess, rather than knowing anything about anything about that airport or this particular NOAA charting standard.  Pretty cool that Google Earth gives us the sort of precision to see things as precisely as you were able to measure it.

Per @RalphJ's suggestion, I measured the distance from a landmark (specifically, the kink in the river NE of the A in Alpine) to the runway in Google satellite view:

(Image from Google maps, Imagery ©2023 Airbus, Landsat / Copernicus, Maxar Technologies, USDA/FPAC/GEO, Map data ©2023)
This gives 8300 feet, and measuring the same distance in the new chart it is also 8300 feet. So this appears to be a correction of a previously incorrect location for M45, and not a shift just for cartographic convenience or anything like that.


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In a push-pull twin, which engine is number one?
I know this is kind of a silly question, but I'm curious.
On a "standard" multi-engine airplane, the engines are numbered from port to starboard, with the furthest port engine being number one. But in a "push-pull" twin-engine airplane like the Cessna Skymaster, which engine is considered "number one"?

@757toga Well, who decided that the left engine is always "#1" in a conventional plane?

Probably some pilot or engineer from the early days who's name is forever lost to the sands of time...

With the port/starboard engine numbering, if they had copied ship numbering schemes we'd have even numbers on the left and odds on the right, just to really confuse people.

@757toga Listening to ATC recordings on YouTube and LiveATC, I've heard them refer to engines by number, even on twin-engine Boeings. They will usually clarify by saying something like "We're having trouble with engine number one; the left-hand engine".

If Cessna didn't designate them as #1 and #2, then there isn't one.
The convention Boeing uses is Left-to-Right and Front-to-Rear for numbering: the left engine is the #1, the forward doors to the aircraft are the #1 (1L and 1R) doors, and things work toward the rear from there (2L and 2R, then 3L and 3R, and so on).  And obviously seating rows start with #1 in the front and get ever higher numbers toward the rear.
So by that convention, the forward engine would be the #1, which would probably be intuitive to most people.
Interestingly, Lockheed used the same front-to-rear convention for numbering the guns on the AC-130, where the #1 and #2 were the twin 20mm cannons up front, and stepping up to higher numbers working toward the rear.  In the AC-130U, which didn't have twin 20's but a single gatling gun up front, that gun was the #1, the 40mm was the #2, and the 105mm was the #3; in the older AC-130H I think they didn't renumber things as the small gatling guns were removed, so I think they still referred to their 105 as the #7 gun, even though there weren't 6 guns installed forward of it.  I assume that the AC-130J uses the same convention, but I'm not familiar enough with those to state anything definitively there.

@757toga  Yeah, thus my first sentence -- if Cessna didn't designate a #1 or #2 engine, then there isn't one, period - dot - full stop.  Everything after that is just what-if-ing and "if you were to apply the Boeing or Lockheed conventions to this Cessna, here's the result you'd end up with."  Not suggesting that there's a reason to apply those conventions there.


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How can a pilot help someone with a fear of flying?
I have a cousin that has a pretty bad fear of flying. I've been trying to get her to fly with me for a while. My question is: If I succeed, what should I do to make the experience better?
I've tried to find advice online, but the only resources I can find are either geared toward helping yourself get over a fear of flying, or what to do if you're a passenger on a commercial jet with a scared friend. I'm looking for something a little more pilot-specific.

There's a great answer here BTW if you choose to let her fly:  https://aviation.stackexchange.com/questions/3378/how-would-you-brief-passengers-who-will-try-flying-your-plane?rq=1

Seems like even the best pilots might want to let someone with training in psychology, psychiatry, therapy, or something similar address problems with the mind and emotions. To me this is like asking how a therapist can help recover from a stall.

By starting a youtube channel?  Comments on videos from https://www.youtube.com/c/74gear and https://www.youtube.com/@MentourPilot frequently include ones saying that learning more about flying helped people overcome fears they had of flying, or be less nervous.  IIRC, a comment on 74gear's channel reported having been nervous and showing it, and this guy sitting next to them started talking about aviation and explaining stuff that was happening, and that it helped.  (And that it was Kelsey; the nervous passenger had found his channel later and left a comment.)

@ToddWilcox, you said it better than my since deleted comment!

Why do you want her in particular to fly with you? If I had a professed bad fear of something and my cousin kept asking me to participate in it, I'd be pretty upset with them.

@AzorAhai-him- I might have a different relationship with my cousin than you do with yours, because we laugh and joke about it all the time. Also, she's said that she hates being so scared when she has to fly commercial, and would like to get over her fear at some point.

Well, "she asked me help her get over her fear of flying by taking her up" lends a different vibe to your intro paragraph.

To be fair, general aviation (Cessnas, private jets, etc) has many unsafe pilots. BUT you can make it safe with enough rigor and a conservative weather no-fly policy.

I wonder if taking your cousin on a simulated flight (via some kind of flight simulator) would help acclimate her to what it's like, in a safe environment that she can step out of any time she needs to?

Take them for a ride early in the morning, just after sunrise, or at least before 9AM. The flight will be silky smooth.  Be very smooth yourself. Enter and exit turns gently, avoid any sudden pitch moves. Fly like you have a case of nitro-glycerin in the seat beside you.
Take them through the preflight and all the preparations. In the air, tell them what you're doing in a relaxed travelogue soothing voice. It they think you're nervous, it'll wind them up tight. Calm confidence in your voice will work wonders.
Get them focused on the sights outside at first.
After about 15 min, ask them if they want to take a little try at the controls, just the wheel/stick and talk them through a few turns etc. Don't push if they say no.
Mostly though, smooth air, smooth flying, and calm voice/demeanor are the main things.

"Fly like you have a case of nitro-glycerin in the seat beside you."  My favorite is: "drive like you are on an icy road to grandma's for Thanksgiving with a bowl of hot gravy in your lap."

"Press the pedals like there's a raw rotten egg between your foot and the pedal."

Also pre-flight: make it clear that they can abort any time they like. "If you feel you need to be back on the ground, tell me and I will get us back as quickly and safely as I can."

The McDonald’s coffee thing being frivolous litigation is a myth. https://www.vox.com/policy-and-politics/2016/12/16/13971482/mcdonalds-coffee-lawsuit-stella-liebeck

Fair enough. But for the purpose of the gag it works.

Similar advice applies to taking nervous guests on a sailboat for the first time.  Choose smooth conditions, avoid sudden maneuvers and surprises, aim for as boring an experience as possible, if you want them to ever step aboard again.

The reasons and/or motivators for a fear of flight vary largely from person to person.  Some people fear it because of motion sickness, others don’t like air turbulence or the idea of dying in an airplane crash is particularly traumatic and frightening.  I once flew with a man who only became scared on final approach because he didn’t like the sight of the runway and the ground approaching.  People vary greatly in their perceptions of the world around them and, combined with a wide variety of experiences, can suffer trauma and unpleasant sensations, even in seemingly innocuous or perfectly safe environments, no matter how irrational they might be. A six year old child may be terrified of a friendly dog due to a traumatic event a year earlier where she was bitten by a different one.  She now associates canines with fear and being bitten.  Likewise flying can be a painful if they had a first bad experience or saw a news story about an airplane crash.  Provide them with fun, positive experiences associated with flying they can get over that, or at least assuage most of their fear.
The best advice I can give you is:

Ask this person why they don’t enjoy flying.  You can’t help them if you don’t know what bothers them so much.

DO NOT DISMISS THEIR FEARS.  Doing this only makes it worse and could potentially cost you a friend.

Suggest ways to counter their fears.  The best way to approach this is to identify positive ways they can assuage we their fears.  For instance if the fear is rooted in airsickness, give them some good ways to minimize this through breathing deeply and look outside the aircraft.

Enable them to overcome their fears, if they want to, in a positive and fun environment.  You don’t want to force them into an environment, where they’re scared, barking orders at them like a drill sergeant.  Instead, provide an environment in which they can overcome their fears in a safe and enjoyable way. And when they do, give them a lot of positivity.  It’s a great way to allow them to clear obstacles in their life and pave the way to something a lot better.

If you take them flying, remember to do so in an enjoyable manner. Like John K said, above, fly the airplane in a smooth and non-startling manner, taking into account the things that your friend may have told you that scare them about flying.  DO NOT discuss negative things like gruesome details about accidents, etc. Remember the key here is a positive experience to nullify any negative feelings they experience about flying.  Also make the flight part of something that’s fun about aviation. Take them out for a good hundred dollar hamburger. Fly over a national landmark.  The experience of flying in a small airplane is quite different from that of a commercial airliner, which I’m sure they’re used to. You’ll see a lot more of the world and you’re down lower so there’s more to take in.

Another one I've heard is that they don't like the fact that they can't just stop and get off whenever they want, like a car.

The main problem lies within the irrationality of the fear of flying. While there may be many reasons to be anxious about flying, none of them are "statistically reasonable", with the exception of unwillingness to travel by air because of motion sickness, which I do not think classifies as fear of flying per se.
Since the fear of flying is irrational, it is highly unlikely it can be overcome with reasoning. The subject has made a profound internal analysis that deems flying terrifying. Facts about the safety of air travel will not help, and neither do reassurances of the multiple layers of safety within the industry. The prognosis is not good, so to say.
Have you inquired your cousin what is the reason for her phobia? That may give you some clue as to how to approach the subject, keeping in mind what I wrote above. Above all, I certainly would ditch the idea of persuading her to fly with you as any sort of a goal.
My suggestion is to offer her a chance to familiarize herself with aviation at her own pace, with no binding schedule and, most importantly, a chance to bail out at any point (pun intended). This introduction should be done in steps, that can, and preferably should be distributed to separate occasions:

get her to visit the airfield, explain how GA stuff works there. Do not talk about flying yet, unless she specifically asks about it. Explain ATC (even if your field didn't have it), who operates the field, how many people buzz around. You  know, general stuff, sorta like in a Richard Scarry book.
introduce her to the planes on the tarmac. Their features, why they are different, and why they are same etc. Dig in a bit deeper into the subject than last time. Show your expertise, but don't go in too deep.
get her in the cockpit, show and tell what's what, and why. Gauges, yoke, pedals, flaps etc. Don't rub in her face, but every now and then, when appropriate, drop a few lines on the safety aspect of doohickeys in the plane, such as "we use flaps during approach and landing because that makes it safer to fly slowly".
show how a preflight is done. Like a proper preflight with planning.
if/when she's comfortable take her taxiing around the field. If ATC is present and traffic situation allows, they'll surely let you even taxi to and along the runway for familiarization.
should all go well, she may be ready to take a flight in a while. Make a small sightseeing flight, pick a nice familiar place to go and see, something she can relate to safely. Do not fly closed circuit with a person with fear of flying.

Main point is to explain to her you have this plan  with the general steps above, and that at any point she can stop, and there will be no persuasion, picking or anything negative. No strings attached.
If your local field has a cafe or a good sighting area, that's a very good starting point: go planespotting first (and secretly hope no-one effes up while you are watching). If there are night operations, do a night picnic, airfields are mesmerizing places by night. You should aim at making flying more interesting and exciting than it is frightening.
And remember: if her phobia is anything but mild, it'll most likely be way out of your league to fix. Fear of flying is usually quite impermeable.

I don't think it's irrational in the case of private pilots (as opposed to commercial air travel). See various questions on this site regarding accident statistics.

According to her, it's because of a lack of control. She says she's slightly nervous even riding in a car with someone else driving. I've offered to start out by taxiing around the airport without actually taking off the first time.

@Reid you are absolutely correct on GA not being safe, but I consider fear of flying to be a general fobia of flying, not just flying in small planes. Being afraid of that is just common sense

@HiddenWindshield so it's more of a trust issue laced with fear of flying maybe. That might be resolvable.

FYI the spelling is "phobia". Yes, English makes no sense (although this one is a loan-word)

Yea, it can be confusing at times, especially for a person mostly using a phonetically consistent language

You can offer to help them, but putting pressure on them to fly might actually make the problem worse. You can only help people that want to be helped. As others have said if they do want your help, be as careful as you can. Any bad experience will only make the issue worse.
Many people are afraid of flying. I used to work for an airline and was pass riding back to MIA. Knowing I was an employee that sat a pilot beside me who was over his hours and had to ride back to MIA. He explained to me while he loved flying planes, he was scared of riding in them when he was not the one at the controls. For the entire flight he had a white knuckled grip on the arm rests, was staring straight head, he was pale, and would only grunt in response to questions. Once we landed he was fine. So your friend is not alone in their fears.

She's said she does (eventually) want to get over the fear.

Frame challenge: Don’t take the cousin flying.
The OP clearly wants to take the cousin up, e.g. “I’ve been trying to get her to fly with me for a while”, “if I succeed” (emphasis added).
But there’s nothing in the question or the OP’s comments to indicate that the cousin wants to go flying with the OP, a private pilot.
There is plenty about how the cousin has a fear of flying, e.g. “she’s said that she hates being so scared when she has to fly commercial, and would like to get over her fear at some point.” But that is all about commercial air travel, which is quite a bit different than flying with a private pilot: it has a purpose other than recreation and it’s significantly safer.
(One commenter says “Well, ‘she asked me help her get over her fear of flying by taking her up’ lends a different vibe to your intro paragraph”, which would be true, but I don’t see how that’s an accurate reading of the question and comments.)
Another thing worth noting is the claim that “we laugh and joke about it all the time”. It is a very common tactic for women to use humor to deflect a conversation when they don’t feel comfortable explicitly saying no. So I’m quite skeptical this should be taken as an indication that the cousin wants to fly with OP.
In my view, the best reading of this question is that the OP wants to take the cousin flying, the cousin is not interested, and the OP is missing or misinterpreting the cues indicating that disinterest. If the cousin actually wanted to go flying with the OP, she would have stated that clearly and explicitly, and the OP would have relayed that clear and explicit interest in the question as originally written.


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Is it common practice to omit some points in an airway?
An airline filed the following flight plan:

[...] IRK.J96.SLN..LANCY.J134.PKE [...]

The cruise altitude was around 30k feet.
Waypoints in J96 are:
LAX PDZ YCDIL PKE* LANCY* DRK KEYKE GUP CIM GCK SLN* AGENT KIDER IRK* NORIS PIA JOT

J96 spans between 18k-45k feet.
So it means that someone put a direct in the middle of an airway. Why was the flight plan not filed with an all-airway routing like this:

[...] IRK.J96.LANCY.J134.PKE [...]

Is it common practice to omit some points in an airway?

Guessing only, but maybe the direct is frequently approved and thus planning on it better reflects what will happen? It’s only a couple of miles, though...

It's 967 miles and as far as I saw it's not that common to fly direct

I meant the shortcut is only a few miles shorter than following the airway... and hey, all I gave was a random possibility. Without speaking to the original planner, chances are we’re not going to find out the rationale behind the plan, anyway (or whether it was simply a typo or other glitch, for that matter).

Objection your Honor, the question calls for speculation...

Indeed we would have to speak with the original planner. I am new to industry, so I thought maybe it's a common practice to omit some points in the airway. If it's not then it's also valuable knowledge :).


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Flight plan departure procedures vs real life departure procedures
In the flight plans there are included departure procedures. However, sometimes something can change eg. different runway is assigned by ATC and then departure procedures in the flight plan is invalid, because SIDs are assigned to the runways.

Are flight plan amendments send after such change?
Does it happen often?
How airline dispatcher knows which departure procedure to fill in the flight plan if he doesn't know which runway will be used in the future or what will be the wind direction etc.

Only some countries require you to include the SID in the flightplan. In many countries, you will just list the first en-route fix, and ATC will assign a SID prior to departure. Also remember that most airports don't have SIDs.

1) Not to my knowledge, these are short-term deviations from plan that do not require an updated plan (similar to ATC offering direct routings - shortcuts).
2) Not sure. What qualifies as “often”?
3) Experience, local and airport procedure knowledge and a weather (wind!) forecast go great lengths in predicting departure runways and routings.

When it comes to flight planning, dispatchers are the best in the business. That is literally what they are payed to do. However, they, for obvious reasons, don't always guess the correct runway. Luckily, it doesn't really matter. As long as the aircraft has the performance to take off from the assigned runway (which would be calculated in the FMC or EFB) the new runway can likely be used without a Departure Procedure  or SID change. Runways are switched quite often, but it's not a big deal.
This is because SIDs almost always work for any runway. For example, look at the BROAK1 at KPHX. You can easily see that each runway has slightly different departure headings and early turns, but all join together at the fix BROAK for the rest of the departure. So, if a crew was assigned a different runway, they punch the new assignment into the flight plan on the FMS and off they go.

"This is because SIDs almost always work for any runway." While that may well be correct for the United States, it certainly it not in most of the world


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How is data exchanged between Eurocontrol and FAA?
Let's say I want to fly from Europe to USA.
Then (probably):

I'm filling flight plan message(FPS) and it goes to Eurocontrol system.
It is somehow transmitted to FAA. How?

Flight plans are distributed to all air traffic control units that will be providing services along the route over the Aeronautical Fixed Telecom Network (AFTN).

Nowadays most communications between Europe and the US is over AMHS (https://en.wikipedia.org/wiki/Aeronautical_Message_Handling_System)


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Does wing paint colour improve airplane fuel efficiency?
If birds that fly very long distances like seabirds have darker colours on top of the wings and lighter colours underneath the wing, is it possible that painting airplane wings similarly may improve fuel efficiency?

It would probably do more to hide them from predators.

I hope so! I am getting my plane painted next month. Getting my ratty 30+ year old removed and some nice smooth stuff put on. Lighter cooler, less solar heating, should keep the fuel cooler, no?

@CrossRoads unless you have some overheating issue, heated fuel is beneficial for engine power.

Perhaps, but cool fuel is more dense yes? So more horsepower can be generated from the same gallon of fuel.

You'd have to calculate fuel $\alpha$ versus the increase in enthalpy. I was taught that heated fuel was beneficial, at least when dealing with JP4

I just came across this in another forum (cardinalflyers.com), backing up the need for keeping wing tanks cool:   Using a volumetric temperature expansion coefficient of .00053 (Gasoline Fahrenheit) and starting with 50 gallons at 60 degrees, once it gets to 110 degrees (with some sun baking) the volume changes by 1.35 gallons.

Please read this article in Journal of Thermal Biology - this colouration differential causes air pressure differential between the top and bottom of the wing, not unlike the force that drives the crookes radiometer. The name of the article is ‘Thermal impact of migrating birds’ wing color on their flight performance: Possibility of new generation of biologically inspired drones’

I would doubt it.  The main issue with colour choice with airplanes is heat absorbed into the structure in sunlight, which tends to discourage dark colours.  Stand around a black painted light airplane on a hot sunny day and listen to the crinkle sounds as the skin expands and contracts as clouds put the wings in and out of shade.  If there was any effect, the distortion of the structure from heating (skins wrinkling) would reduce efficiency, if anything.
Aside from that, not a big problem for the structure with aluminum, but it is a problem for composites, especially room temperature cured homebuilt composite airplanes, where the sun can heat the skin to the epoxy's transition (softening) temperature.  This is why composite aircraft are almost always white, and if you see dark colours it will be on a structure that was post cured (heated while curing) to raise the transition temperature and make the finished structure more tolerant of high temperatures.

What do you think of the idea of using recycled aluminum, that would have dark colours/impurities already in the material, on the top of the wing, and pure reflective/white aluminum on the bottom? This would increase the pressure differential between the top and bottom of the wing, increasing lift and improving fuel efficiency, right?

Well you might as well paint the top flat black and the bottom white.  In the article you linked, they are theorizing that a hot upper surface reduces the density of the air right against the surface and this creates a small reduction in skin friction.  Could be.   My guess is any beneficial effect is too small to be significant on a wing moving at high speed, but it would be an interesting topic for someone's PhD thesis.

Birds colors are made to protect them from predators. Just like military fighter jets. They have light colors on the bottom, so they will be less visible agains the sky when looking at them from below. Darker colors on top like camouflage, on the other hand, will hide them against the ground when looking at them from the sky.
I really doubt it will help you to save fuel. If you want to save fuel, you better not paint the aircraft at all to save weight. They did it during WWII. That's why those mustangs where all made in polished aluminum. The only part that was painted was the top of the nose, to protect the pilot from the glare.

Check out : https://www.sciencedirect.com/science/article/pii/S0306456517300712


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Why are winglets swept back and not front?
A winglet is defined by its airfoil shape, profile, sweep angle and height. In case of the sweep angle, why does it always mean that the winglet is swept back. What is the disadvantage of having a front sweep angle

Related question: https://aviation.stackexchange.com/questions/2360/what-are-the-advantages-of-a-forward-swept-wing-over-a-rearward-swept-wing

A good subquestion would be why a sweep angle not equal to zero?

A winglet makes lift like a wing. That's why it's called a wing...let.  It's basically a sail (originally they were called "tip sails") designed to exploit the otherwise wasted circulation of air from bottom to top around the tip, placed so that the local flow curling around the tip strikes it at a positive angle of attack.  It makes lift/thrust and, being a wing, creates a downwash while doing so, which means some of the circulation is being redirected back the other way (an "outwash" in other words).
So the overall effect is the vortex field is weakened, and some its energy is used to make lift and/or thrust.  If the winglet is straight up, its lift component is straight inboard and forward, and is purely thrust and a (wasted) bending moment on the winglet root (which leads to angled winglets).
If it's angled, its lift component is a combination of vertical lift that contributes to holding up the plane, and thrust.   So the dihedral angle is a function of how much the designer wanted the winglet's lift force to be extra lift and how much was to be thrust, the resulting angle being a compromise sweet spot between inboard lift and vertical lift in that particular wing's tip flow pattern (nobody seems to use straight up winglets any more).
The sweep angle is for the same reason the main wing is swept, to reduce high Mach# drag (remember it's not just a fin "blocking" airflow;  it's a wing making lift like the main wing), and also to place the winglet in the optimal location in the circulation for exploiting the energy in the flow.

Simply because it's easier to pull something bendy than to push it.
When you load a forward swept aerofoil, it will bend in a direction that increases the load, so it has to be stronger (and heavier) than a rearward swept aerofoil.
The technical term is 'aeroelasticity'.


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What plane is this, appearing in the movie Rampage?
The plane's registration number is barely visible. Unfortunately it's the best quality I could find.

It's a Boeing C-17 Globemaster III. The tail markings appear to be those of the 437th Airlift Wing, US Air Force (thanks to TomMcW for the unit identification).
To answer the question yourself, note that you can see the US flag on the vertical stabilizer and the word "Force" behind the cockpit window. Wikipedia has a list of planes flown by the US Air Force and, although the list is quite long, it is categorized by mission, which cuts down the options quite a lot – the plane obviously isn't a fighter, for example, and, conveniently, "cargo" is early in the alphabet so close to the top of the list.
The serial number 2300 (or 7300?) painted on the nose doesn't correspond to an actual USAF C-17; it was probably temporarily renumbered while filming.

Though I'm slightly confused that the serial number on the nose (2300 or 7300) doesn't seem to match anything on this list.

I think the number is "fake", as in "put explicitly for the movie and then removed"

If i were you id search for something like "military aircraft with four engines" in Google images and Google and move from there

@AliErdem That is surprisingly effective, given the number of different four-engined military planes there are. Or maybe Google is pushing C-17s up the list because I've done several searches related to them in the last few hours!

...The "fake number" assumes that they used a real airplane for the shot, instead of a 3D model of some sort.

It appears to have the tail band from the 437th Airlift Wing out of Charleston.

Thanks, @TomMcW! I tried half-heartedly to identify that but there are enough units flying C-17s that I gave up.

@AliErdem I don't see how that is a useful comment

@Federico I think it's fine. My answer gives a way of identifying the plane; Ali gives a simpler way.


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Why isn't Vy equal to Vmd?
$V_{md}$ is the speed where the rate of sink is the lowest. So if you add full power, it should be the speed with greatest rate of climb, namely $V_y$.
But we also know $V_{md}<V_{bg}$ according to this speed polar graph as a general rule
If I connect the inequalities, I have $V_y=V_{md}<V_{bg}$. In the particular Cherokee I'm trained in, $V_y$ is 75 knots and $V_{bg}$ is 69 knots. So where in the reasoning am I wrong? Why isn't $V_y$ equal to $V_{md}$?

Vy includes engine/prop efficiency factors, so it can not be directly compared to glide data.  Vbg is the best speed for DISTANCE, which is what you want to make your emergency landing site if you have an "engine out". Vmd will give you a lower sink rate, but you will not glide as far.
Interestingly, if you have to glide INTO the wind, best glide speed will be FASTER than Vbg to make up for loss of groundspeed.  Best glide speed there for is the optimal ratio of altitude given for ground gained.


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Why is best angle/rate of climb indicated in airspeed?
I understand the difference between best angle of climb $V_{x}$ and best rate of climb $V_{y}$. When I take off I would aim to maintain one speed or another depending on what I want.
But I don't understand why it's measured in airspeed, instead of pitch angle, which would seem more intuitive.

Remember that Pitch plus Power equals Performance. If you are aiming for a specific performance (e.g.  climb rate) then it depends on two things. Power will vary with altitude and temperature, so the pitch will be somewhat different in different environmental conditions.

This is done on large jets... immediately after lift-off and on go-around, the flight director will give you a pitch command that will maintain V2+some margin (V2 on engine failure). Airbus calls this the Speed Reference System. It actually is an important safety measure for countering somatogravic illusions.

Because determining Vx and Vy has to do with the specific aircraft, specific power output of the engine, thrust from the propeller, etc, which is often a function of pressure altitude and airspeed.
Remember that Vx represents a situation where the aircraft has the MAXIMUM EXCESS THRUST meaning a situation where the difference between the maximum thrust available and and the thrust required to neutralize drag force and maintain straight and level flight is the greatest.

Images courtesy of BoldMethod
Vy on the other hand is the point where the aircraft has the MAXIMUM EXCESS POWER available to it, translating into the greatest change in altitude for a given period of time by simple conservation of energy considerations.

Images courtesy of BoldMethod
The airspeed where Vx occurs increases as the pressure altitude increases.  Conversely Vy decreases as pressure altitude increases.  This is due changes in power and thrust outputs with increasing pressure altitudes.  Vx and Vy eventually equal each other at the aircraft’s absolute ceiling, since there is neither any more excess thrust or power available here for climbing.

Thanks. But the same could be said about pitch angle as well (dependent on power output, aircraft, ...) My question is, why isn't the Vx Vy on AFM/POH indicated in pitch angle, instead of airspeed.

See the first paragraph of my answer.  It works out that those values are a function of pressure altitude and airspeed as they are dependent on the amount of power and thrust an engine can produce respectively.

Would it be correct to say that, say, a "best-rate-of-climb pitch" would depend on aircraft weight much more than the best-rate-of-climb airspeed does? If so, I think that would answer @Hot.PxL's question.

No!  There is no specific pitch angle here, only a particular airspeed in which the greatest excess thrust or power is available for climb.  One would apply full power during climb and pitch the aircraft to maintain these specific airspeeds in order to obtain the best angle of climb or the best rate of climb.  Vx and Vy can vary with weight, however, on larger aircraft, as they have a direct effect on the amount of induced drag created, which in turn affects how much excess thrust or power is available for climb.

@HenningMakholm I understand what you are trying to say, and it does make sense to me. Thanks

@CarloFelicione I feel definitely there is not a single best-rate-of-climb-pitch. There is not a single best-rate-of-climb-speed as well, I think. Because if you close the throttle down all the way, you would be in the same situation as you'll be at absolute ceiling, where $V_{x} = V_{y}$. So that means $V_{x}$ and $V_{y}$ also depends on the throttle setting. But it's much less dependent than pitch angle, so we use that. And also the fact that everyone uses full throttle at take-off, so the $V_{x}$ are really that at full power.

In reality, Vx does produce the higher climb angle, and is used to clear obstacles.  This is the application.  In the theory, one must also consider the contribution of engine thrust to the climb.  Less efficient, but may be helping the plane rise at a greater rate per distance covered.  Interesting to note, Vx in the Cessna 172 is around 55 knots, 10 less than Vbg!

@Hot.PxL Correct.  Vx and Vy vary with aircraft loadout and pressure altitude.  They are by definition, defined where the throttle(s) are wide open, since this offers the maximum amount of both excess thrust and engine power to climb with.  Again you need to remove the relationship between pitch angle and Vx or Vy as they are not related to that (though in reality they do have a relationship with angle of attack, since this affects induced drag, however this is accounted for).  They are a function of airspeed.

"Conversely Vy decreases as pressure altitude decreases." - this is not 'conversely', this is 'likewise' :) You wanted to say 'as ... increases'.

A very simple practical reason is that Vx and Vy speeds can be easily monitored as the pilot is climbing away and controlled with the elevator.  This useful information is in the POH to be used by people who are quite busy at the moment, there for it is expressed in a user friendly form.
Climb angle, as a matter of interest, could be studied
for a variety of engine, prop, weight, flap setting,
etc., but what the pilot needs on the spot is V at full throttle climb.

Let’s say you have an engine problem, or it’s hot and your performance is negatively effected. The angle of attack will be very different to get best climb, but the airspeed will be the same as if you have lots of power.

Pitch angle only corresponds to an angle or rate of climb at a particular excess thrust.
Consider the typical stall exercise: you pull the engine to idle, then apply more and more elevator to try to maintain altitude, thereby pitching up and simultaneously reducing airspeed. At one point, airspeed drops to the point where you lose lift, and you fall out of the sky, despite the fact that you are nose high.
Once you apply power and push the nose down a little, it again becomes easy to establish a climb to regain any altitude lost.
Heck, consider how you slow an airplane down in the air, by raising the nose without having excess thrust.
If rate of climb (expressed as either best angle or best rate) related only to pitch angle or angle of attack, then instead of slowing down, you'd start to climb and maintain that climb as long as the pitch angle is unchanged, no matter the power setting. That's clearly not happening, at least not for long, so there must be something else to determine whether the airplane actually climbs or descends. That factor, as already mentioned, is (excess) thrust.
Therefore, expressing Vx or Vy in terms of pitch angle would require taking into account the amount of excess thrust available. Accurately estimating that directly is non-trivial, at least without specific instrumentation, and would also likely require the pilot to memorize a whole table, rather than a single (or two) indicated airspeed(s). During a high-workload phase of flight, including take-off and initial climb-out, every little bit that adds to the mental workload of the pilot risks increasing the workload beyond the pilot's capabilities.
If instead you aim to maintain a given indicated airspeed, you will be at a point of the power curve where all the factors line up for that airspeed, regardless of the external conditions (pressure altitude, wind, etc.). If airspeed drops for any reason, you pitch down slightly to pick up more speed and maintain the climb; if airspeed rises, you pull the nose up instead to slow down (trading airspeed for climb angle). You're using the pitch angle to maintain an airspeed, and the only instrument you need to pay very close attention to is the airspeed indicator.


text:
Why don't LPV approaches use WAAS GPS for DA
In an LPV approach, the WAAS GPS (not the barometric altimeter) is used to generate the vertical guidance. But the decision altitude for going missed is determined using barometric altimeter. Why isn't the DA using WAAS GPS for consistency? This way the DA will be the exact same point on the glide slope no matter what the field temperature is.

I'm not sure, but usually SBAS corrected altitude isn't shown to the pilot at all, right? All aircraft I'm familiar with only allow setting minimums based on barometric (DA) or radio (DH) altitude.

Just like an inner marker on an ILS approach, yes?

I'm pretty sure it's an artifact of the conservatism applied to the certification of WAAS LPV approaches. From a certification standpoint, the assumed vertical precision of GPS is not considered adequate compared to baro alt, even if technically it is.
With smartphones having GPS antennas that can resolve position down to inches, you could probably fly an LPV approach using an app on your phone (if someone made one) with more precision than a TSO'd aviation system, but the phone isn't certified.
It takes a long time for change to work its way through the system, and the technology tends to run quite a bit ahead of its application in aviation.

I don’t think smartphones are WAAS equipped or have that accuracy.  This makes me imagine a grisly scene of NTSB and local LE coming up on an aircraft accident with the smashed and burning wreckage in a ravine 300 yds before the approach end of a runway in blinding snow.  Near the lifeless, bloody hand of what was once the captain, investigators find a smartphone with a Verizon ad playing, saying “Can you hear me now?”

Yes a smart phone can now resolve 3D position down to centimeters, whereas the aviation equipment is stuck with its legacy cert requirements. An new GPS antenna was developed a few years ago that made this possible. That's why delivery drones can deliver a package to your front door. Not saying you would ever try it.

@JohnK Do you have a source that GPS in smartphones is accurate to that level? I haven't seen anything better than a few meters claimed in any reputable source, and that is just for lat/long, not altitude.

In any case, drone deliveries are operated under part 135, so presumably they would need to use similar certified GPS just like any other aircraft that requires an airworthiness certificate?

It was an article about the development of a new antenna for cell phones developed IIRC by the University of Texas. I'd have to dig it up.

One thing never to forget in aviation is redundancy - if possible never trust a single system - better have two or even more independent sources to crosscheck their data. Such as verifying the correct GPS height with the barometer to be really sure you are not too close to the ground.


text:
GPS-based IAP at alternate airport
I'm reading AIM 1-1-17 section 5. (c). I understand that the current regulation allows un-augmented GPS (non-WAAS GPS) to be used at either destination or alternate, but not both. But the chapter goes on saying that

At the alternate airport, pilots may plan for:
(1) Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
(2) LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approved barometric vertical navigation (baro-VNAV) equipment;
(3) RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro-VNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program.

What do the extra items here signify? The alternate weather minimum is still 800-2, so these don't have anything to do with that, right? If so, are these items trying to exclude certain types of GPS approaches that aren't available as alternate?

The 800-2 is for the airport to qualify as an alternate. If you divert there, you fly whatever approach makes the most sense, to its published mins.  The planning requirement is separate from flying the actual approach.

@757toga  I get all that; my point above is that 800-2 (or whatever other number one gets from those various sources) applies preflight when considering using the airport as an alternate, and not when actually flying an approach at the alternate.  I know you understand that already; some readers may not.

Offhand, it looks like they exclude LPV minima and minima that use an RNP below 0.3 NM.  Those would typically be well below 800-2, but there would usually be an option with higher minima for the same approach (i.e. most RNP approaches have a 0.3 minima in addition to lower minima for tighter RNP values, and most approaches with LPV minima have higher mins for methods like LNAV/VNAV or LNAV-only).

While it’s common for approaches to have circling minima, not all do for various reasons.  Likewise, while it’s common for RNAV approaches to have LNAV minima, not all do.
#1 says that you can use an RNAV approach if it does have either LNAV or circling minima.
#2 says that if you have Baro-VNAV, you can use an RNAV approach if it has LNAV/VNAV minima.  This could come into play if the approach has neither LNAV nor circling minima.
#3 is similar but for RNP.
If approach doesn’t pass (at least) one of these three tests, you can’t use it to qualify an alternate.


text:
What airspace class is the New York Hudson/East River SFRA airspace, and what is its visibility requirements?
In general, the airspace below a Class B shelf is Class E airspace until 1200' or (more often) 700' AGL, and then Class G to the surface.
Immediately surrounding the Hudson and East Rivers in New York City is the EWR/JFK/LGA Class B airspace, which has a floor of 1500 MSL in that area. Over the Hudson River the floor drops to 1300 MSL; over the East River the floor remains 1500 MSL, except within the LGA surface area where the floor is 1100 MSL.
Over the two rivers and below the Bravo floors are the Hudson and East River Class B Airspace Exclusion Special Flight Rules Areas, which are defined at 14 CFR 93 subpart W.

This is excluded airspace is, of course, not Class B, because it is explicitly excluded from Class B airspace. Is it Class E and/or G airspace, as expected for other airspaces below the Bravo shelf? Or is it a "special" non-Class E/G airspace area?
Practically, what are the visibility and cloud clearance requirements in this SFRA airspace?

Having special flight rules in Part 93 doesn't mean that the regular flight rules of Part 91 don't still apply. The SFRA is within the faded magenta line on the sectional chart, indicating Class G up to 700 and Class E above that. In fact, it is within the New York E5 airspace as listed on page E-373 of the current JO 7400.11E.

AEA NY E5 New York, NY
That airspace extending upward from 700 feet above the surface within an area bounded by a line
beginning at lat. 40º49'00'' N., long. 73º17'02''W., to lat. 40º36'00''N., long. 73º12'27''W., to lat.
40º29'42''N., long. 73º30'53''W., to lat. 40º29'43''N., long. 73º52'12''W., to lat. 40º15'00''N., long.
74º00'00''W., to lat. 40º14'32''N., long. 74º29'47''W., to lat. 40º24'45''N., long. 74º51'22''W.,
to lat. 41º08'17''N., long. 75º00'00''W., to lat. 41º23'15''N., long. 74º43'13''W., to lat. 41º26'08''N.,
long. 73º52'54''W., to lat. 41º16'48''N., long. 73º34'53''W., to the point of beginning excluding the
airspace that coincides with the Wrightstown, NJ, Pittstown, NJ, Philadelphia, PA, Poughkeepsie, NY,
Newburgh, NY, and Danbury, CT Class E airspace areas.
AMENDMENTS 04/15/04 68 FR 70137 (Revised)
Corr: 69 FR 11943


text:
The meaning of RNP
I'm a new pilot working toward IFR and learning a lot of the new terms. Since English is not my native language, I was a bit confused what the actual meaning of RNP is.
I know that RNP stands for Required Navigation Performance. That sounds to me like it's talking about the performance of navigation, but not about the navigation itself. On the other hand, RNAV for Area Navigation is about navigation. How can these 2 words mean the same kind of things, if they are of different kinds?
For example, people talk about "RNP procedures". But what is a "performance procedure"? It doesn't make any sense to me. Shouldn't performance mean capabilities here, like in "CPU performance" or "performance of a computer program"? So what does a "capabilities procedure" mean?
And for comparison, "RNAV procedure" is a navigation procedure, which makes total sense - it's a procedure for navigating around.

Does this help? Possible duplicate.

When there are multiple words in a row in English, usually the LAST word is the noun and everything else is modifying it.  Required Navigation Performance is Performance pertaining to Navigation, and that Performance is required.  RNP Procedures are Procedures relating to the Performance of Navigation that is Required -- or to say it another way, the Procedures related to the Navigation Performance you are Required to have.

FYI, the wording around the use of GNSS (GPS) is very counter-intuitive and reflects the fact that this is a very new field. Acronyms are to be placed in their historical context. This is today federated under PBN: Performance Based Navigation (meaning the navigation aid must guarantee a given position accuracy  or "performance" for the procedure to be used).

Don't take the technical terms too seriously. Technical terms are often poor description of the item, and technical terms in English tend to be particularly bad.
These ones are fairly good for the usual standard in English. It is called “Required Navigation Performance” because there are requirements on how accurate the navigation must be (its performance) and that it has to be able to detect and alert you if it can't ensure that accuracy, and it is kind of implied there is a navigation when there are requirements for it.
For the actual definitions, see What is the difference between RNAV and RNP?


text:
Declaring an emergency - protocols for commercial aircraft
I am researching for a book and would like to know how a commercial aircraft would signal that his aircraft has an emergency.  Not mechanical or violence, but possible biological contamination.
What is the protocol for such an event and what such dialog might exchange between the pilots and ATC?
Any advise would help.
Thanks!
Michael

In addition to speaking to ATC, the crew in such a situation may consult a medical advisory service, such as MedLink, which would allow them to talk to emergency physicians by satellite phone.

Okay, thanks, Zach.  I appreciate your comments.

@Harper the OP never said the pilots would know its biological and understand everything about it. It doesn’t take a Doctor to notice that several people have become very ill very quickly and that they need urgent medical attention.

The procedure would likely be the same as any other medical emergency: get the plane on the ground (which is a thing that pilots are good at doing, and have the training and skills to do) so that the medical crews can handle the medical emergency (which is a thing that pilots are not good at doing, and have neither training nor skills to do)
The initial radio call might be something along the lines of "Mayday mayday mayday, Oceanic 201 requesting immediate vector to LAX for a medical emergency, multiple passengers"

"Mayday" indicates several things all at once.

"Everyone else currently on this radio frequency, shut up."
"I am in the middle of an emergency, therefore I am now the most important person in the sky."
"I will do whatever I need to in order to keep this plane safe. Air traffic controllers, you will get everyone else out of my way."
Saying it three times has no relevance other than to make sure that it's heard and the number three indicates distress in general.

"Oceanic 201" is the callsign of the aircraft.
"Requesting" is used to tell ATC that the crew requires action from them, in this case a vector to a suitable airport.
"for a medical emergency, multiple passengers" prepares the emergency crews for whatever situation they're about to have dropped in their laps.

For further examples of cockpit-to-ATC communication under critical circumstances, you might find it helpful to read the cockpit voice recorder transcript of United flight 232, or other in-flight emergency transcripts.

Thank you, Steve V. for your very helpful response!  I will research your link as well.  Much appreciated!  :D

This is correct.  Also, although the pilot will request vectors if there is time for a request and approval, if the emergency demanded an immediate turn, the pilot will start the turn and tell ATC what they are doing (rather than asking permission).  As noted in this answer, the regulations permit the pilot do whatever they need to save lives, with or without prior ATC approval.  But if time permits, letting ATC give you the vectors is safer, because it gives them time to get other traffic out of your way.

Isn't there a camera outside the cockpit door for them to see who is behind it?

"Saying it three times has no relevance other than to make sure that it's heard and the number three indicates distress in general." - Saying it three times also indicates that you're actually declaring an emergency, rather than simply mentioning the word in some other context. You might say something like "we heard a mayday call" or "request taxi instructions to Mayday Avionics" over the radio, but you'd probably never say "mayday, mayday, mayday" except when declaring an emergency.

@TannerSwett - The day they elect me king of Earth, i'm telling Mayday avionics that they need to change their name.

@TannerSwett there is an avionics company called Mayday‽

@Someone There is, and it really is located on the grounds of an airport, so there's a good chance that someone really has asked Ground for taxi instructions there! (Amusingly, their website says that the company name, Mayday, has "become synonymous for quality and attention to detail in avionics installations and service"... which may be true, but not if it's said three times in a row!)

@TannerSwett I suppose it's fine with the protocol to repeat a distress call three times, but that does not seem like a good name for a company having anything to do with aviation.


text:
In an articulated hub rotor craft, what could cause the blade to flap negatively?

For example in forward flight what could cause the blade to flap lower than parallel to the CF at the front of the aircraft ?

The first thing that comes to mind does not occur in forward flight. That would be a hard landing. Depending on the rotor design and the amount of articulation and the landing gear type, a hard landing can result in some serious problems, notably, Ground Resonance.
In-flight, it may be possible to achieve with a rapid unloading of the rotor (Zero - G) plus cyclic input. One adverse condition which causes negative flapping is Mast Bumping. Usually, if not always fatal. Mast bumping takes a specific set of conditions and control inputs, to take place. It is typically occurs with 2 bladed teetering rotor systems at zero G.

High forward speed at low weight could cause this.

A fully articulated rotor has a coning angle, which is a function of weight and centrifugal forces due to angular velocity. In order to gain forward velocity, the disk tilts forward - at speed, there is usually collective-lateral coupling that tilts the disk sideways, for compensating tail rotor thrust. With such a rotor head, low flapping angles will occur at high tilt and low coning angle due to weight.
The drawing in OP seems not to be a fully articulate rotor head, but a teetering rotor without pre-coning. Such a rotor will have low flapping angles at forward tilt, period.

First, why does the blade need to flap "negatively"?

In forward flight the rotor disk must be tilted forward to produce the thrust required to overcome drag.
In order to tilt the rotor disk forward the rotor blade must be at the lowest point in its range of flapping when it is over the nose (12 o'clock), and at the highest point in its range of flapping when it is over the tail (6 o'clock).
For the above to occur the blade must also be at the neutral point (exactly halfway between the highest and lowest points) at the 3 and 9 o'clock positions.
Therefore the blade must be flapping "negatively" when it is between 3 o'clock and 9 o'clock.

The flapping of the rotor blades in forward flight is primarily controlled by cyclic feathering --- in other words, the pilot must hold forward cyclic to maintain forward airspeed.
I don't believe that mast bumping is a concern with fully-articulated rotors.


text:
In a piston aircraft engine, how much heat must be removed by the oil cooler?
It is pretty straightforward to compute the heat and power generated by the combustion process, given the displacement, RPM and fuel mass flow rate. Similarly, the power exhausted can be computed with knowledge of EGT and conservation of mass.  The difference is dissipated as heat, from air cooling of cylinders and oil cooler.  I'm looking for a rough ratio between oil cooler and cylinder heat dissipation.

Welcome to Av.SE.  Interesting question!

According to Fundamentals of Powerplants for Aircraft, quoted in Mike Busch on Engines (chapter 2), "Other thermal losses" account for 12.2% of fuel energy:

Conduction to air: 7.2%
Conduction to oil: 1.6%
Radiation and misc: 3.4%

The other two areas of loss are exhaust (51.6%) and mechanical (36.2%).
I don't know how "cylinder heat dissipation" would fit into this classification (some combination of air conduction and friction losses?), but looking only at conduction losses gives a ratio of air to oil of 4.5:1.

Agreed. I would like to point out that 'friction losses' do not completely go into an increase of temperature of the environment. Some energy is invested in 'destruction work' of the inevitable wear of the engine...

From 'Internal Combustion Engine Fundamentals', by John Heywood: https://imgur.com/Mh5f9Cn

Interesting to define mechanical energy as a "loss" ;)

I was trying to locate that data for my post but was unable to.  Those numbers are pretty close to what I had always understood in ICEs.  Thanks for posting.

@ymb1 I believe the figure is similar to that of other ICEs 35-40% thermal efficiencies for aviation gas turbines.   Large scale combined cycle gas turbine power plants for electricity production have done even better some even topping 60% thermal efficiency

Typically in an air cooled, reciprocating engine, for the total amount of chemical energy released during combustion, about 40-45% exits the tailpipe as heat in the exhaust gases, 25-30% of that energy is transferred to the propeller through the crankshaft as mechanical energy, 15-20% or so exits the engine from cool air flowing through the cowling over the engine block, and the final 5-10% is removed through the oil cooler.
SOURCE: THE AIRCRAFT ENGINE AND ITS OPERATION - PWA 109702, pp 19 - Pratt & Whitney Aircraft Corporation, 1949.
I knew I had this in my library somewhere.
If we take a look at an airplane eg an SR-22 on takeoff, the IO-540 engine consumes about 25 gal/hr of 100LL and produces 310 BHP, or is outputting 8.3E8 Joules of mechanical energy per hour. With a chemical energy density of 40MJ/kg for 100LL, this means that about 2.6E9 Joules of chemical energy are supplied to the engine every hour, thus giving us around a 31% efficiency in this example, and that’s about what we would expect.

Do you have a source for this? Seems pretty definitive but could use some supporting evidence.

donwvoted as the answer seems to throw random figures without any calculation nor references.

Those figures are very typical for internal combustion engines.  They will typically only achieve about a 25-35% thermal efficiencies (you just can’t get around the Second Law of Thermodynamics).  More exotic combined cycle engines approach higher thermal efficiencies - in the neighborhood of 50% or so and that’s about as good as you’re going to get.  Yes the rest of that chemical energy just leaves the engine in heat.

If we take a look at an airplane eg an SR-22 on takeoff, the IO-540 engine consumes about 25 gal/hr of 100LL and produces 310 BHP, or is outputting 8.3E8 Joules of mechanical energy per hour.  With a chemical energy density of 40MJ/kg for 100LL, this means that about 2.6E9 Joules of chemical energy are supplied to the engine every hour, thus giving us around a 31% efficiency in this example, and that’s about what we would expect.

@ManuH thanks for giving a clear explanation for the downvote. In the meantime, the answer was updated with sources. Maybe this might be the time to remove the downvote?


text:
How long does a wind shear last?
I've got a job interview next week and the interviewer asked my colleagues this question. I didn't find the answer online, I personally don't think that there is a certain duration for a wind shear because it's a sudden change in wind direction and speed. The question is annoying actually and I really want to know.

Wind shear is sudden for the aircraft that encounters it, that means it is localized (be it vertically or horizontally). That does not tell anything at all about its duration at a given spot for an outside observer.

Don't worry about these kind of things for your interview. Focus on your rounded knowledge and your confidence in your own abilities. Sometimes questions like this will be asked in an interview, where the question doesn't actually make sense or it is some obscure knowledge you aren't expected to know.
If you answer if perfectly the interviewer will suspect you already knew the question would be asked.
If you don't know the answer, say that you don't know. Showing you know the extent of your ability and are willing to be honest to others is very important.

They want to know how deep is your general understanding of W/S.  My answer would be, "What kind of wind shear are you asking about?  Microburst from a thunderstorm cell? Descending through a nocturnal jet (large change in wind velocity at a few hundred feet at night)? Wind shadow shear just above the surface?" (it's not unusual in a jet to hit a little 5 to 10 knot shear at between 100-200 ft when landing, just from the effect of trees and buildings slowing down the surface layer of air) and go from there, based on the research I've down beforehand.
There is no time limit. Could be 5 seconds. Could be half a minute, the time it takes to cross a mile wide microburst at 120 kt.  Whatever. The key thing is to do some googling and read some articles on windshear so you can sound like you've taken the trouble to learn about the topic.
So don't just look up that specific answer.  Become knowledgeable on the phenomenon itself.  That's what they want to see.

I did very well in the interview. thank you sir

At some locations, wind shear can be a nearly permanent condition, such as on the lee side of some mountain ridges affected by steady winds.  On the California coast during the onset of so-called Santa Ana conditions in the fall or winter season, there can be wind shear at the top of the marine boundary layer (typically around 1000' altitude) that lasts for a day or longer before the higher winds reach the surface.  Microbursts, on the other hand, are generally short-lived phenomena, typically much less than 15 minutes.

authors: Vladimir F Героям слава